Updates for OpenTracing-1.6.

[rnburn]

No description provided.

[peterlinnartz]

@rnburn hi Ryan? what's the status here? are there blockers to getting this going again?

[mpbarnwell]

This issue is proving a blocker for upgrading Envoy to use OpenTracing 1.6.0 - I've attempted to fix the merge conflicts in a new fork but there are a bunch of compilation issues, C++ is not in my skillset - is anyone here able to pick it up again?

Our current workaround with Envoy has been to fork it and remove lightstep completely.

[mikhainin]

@tedsuo, @smithclay, @tedpennings - any action on this? I can fix all issues/concerns. We have LightStep with OT1.6 on production for 6 months and it seems to be working. But this issue blocks Envoy from upgrading as this is the last (or one of the last?) tracer library that doesn't support OpenTracing 1.6.
I will be happy to assist with this.